This is the hat that Steve McQueen wore in Tom Horn.
Preferably using a tailors tape either in inches or meters, measure the circumference of your head, 1/2 to 3/4 of an inch above your eyebrows around the back of the head at the position where you wish your hat to be. Do this three(3) times. You will get three different measurements, don’t average them! Give me all three(3) measurements ( ‘measure three times before you cut once).
You can also do it with three(3) piece’s of string. Follow the instructions above and measure the three strings. It is important that the string hugs your head as you would wish a fine hat to fit. Send me the three measurements.